Large variation in nitrogen efficiency among organic and non-organic farms

Agricultural production is requested to be environmental friendly and resource efficient. A literature review of farm surveys and prototype farm studies found that increasing use of N fertilizer and imported feed increased the yields and the productivity of dairy farms, but also increased the N-surplus. We studied the N-efficiency and cause of variation in organic and non-organic commercial dairy farms. Increased amount of purchased-N per ha farmland increased the farm N-surplus per ha on organic and non-organic farms. Increased amount of purchased-N tended to decrease N-efficiency, but not on non-organic farms. The correlation between the N-surplus per unit of produce and N-purchase was weak. The organic farms had lower N-surplus per ha than the conventional farms, had higher efficiency of imported nitrogen and lower N-surplus per unit of produce, leading to an overall better utilization of available N. Within organic and non-organic farm management, the variation in estimated N-efficiencies is larger than the differences between the averages of these two groups